A diode, which is an example of a semiconductor device, such as a Schottky barrier diode (hereinafter, occasionally referred to as an SBD), is a semiconductor device using rectifying action of a Schottky barrier at a Schottky junction between a semiconductor layer and a metal layer. SBDs can operate at a higher speed than general pn-junction diodes, and have characteristics in that a forward voltage drop is small.
For example, in a switching power supply provided with such an SBD, when emergency stop is performed in an emergency, a reverse voltage applied from the n-type semiconductor layer toward the metal layer exceeds a breakdown voltage limit (reverse breakdown voltage characteristics) of the SBD in some cases. There is a concern that if the reverse voltage exceeds the breakdown voltage limit, the characteristics of the SBD deteriorate.
FIG. 8 is a cross-sectional view showing an example of a conventional Schottky barrier diode. A Schottky barrier diode 1 shown in FIG. 8 includes, for example, a semiconductor substrate 2 that is an n-type semiconductor. The semiconductor substrate 2 is configured with, for example, SiC (silicon carbide). In a portion, on one surface 2a side, of the semiconductor substrate 2, a guard ring 6 made of a p-type semiconductor is formed. The guard ring 6 is exposed on the one main surface 2a side of the semiconductor substrate 2, and is formed to a predetermined depth toward the thickness direction of the semiconductor substrate 2. Additionally, a metal layer 3 is formed on the one main surface 2a side of the semiconductor substrate 2 so as to be electrically connected to a part of the guard ring 6. A part of a bottom surface 3a of the metal layer 3 is in contact with the guard ring 6, and the other part of the metal layer 3 is in contact with the one main surface 2a. Thus, the metal layer 3 forms a Schottky junction with the semiconductor substrate 2.
The guard ring 6 includes a p+ type semiconductor portion 6a and a p− type semiconductor portion 6b which have different impurity concentrations from each other. The p− type semiconductor portion 6b is formed so as to cover side and bottom surfaces of the p+ type semiconductor portion 6a. Additionally, a part of the exposed portion of the p+ type semiconductor portion 6a which is on the one main surface 2a side of the semiconductor substrate 2, and a part of the exposed portion of the p− type semiconductor portion 6b which is on the one main surface 2a side of the semiconductor substrate 2, are in contact with a part of the bottom surface 3a of the metal layer 3.
This makes it possible to improve the reverse breakdown voltage characteristics of the junction between the metal layer 3 and the semiconductor substrate 2.
Here, as another configuration different from that of the diode shown in FIG. 8, for example, there is a Schottky barrier diode shown in Non-Patent Document 1. In this Non-Patent Document 1, there is a description about an improvement of reverse surge withstand capability.